Multijunction Solar Cell Segmentation for Radiation Hardness
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Solution Overview
Problem
Current multijunction solar cells for space applications face challenges in maintaining high energy conversion efficiency and radiation hardness over the satellite's service life, due to complex design specifications and unpredictable interactions between material parameters such as band gaps, doping levels, and crystal lattice matching, which affect power output and efficiency.
Innovation Solution
Implementing a multijunction solar cell design with two optically parallel adjacent subcells, where the top subcell covers less than the entire surface of the second subcell, allowing direct exposure of the second subcell to incoming light, and using lattice-matched semiconductor layers to enhance current collection and power output, particularly at end-of-life (EOL).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a multijunction solar cell uses multiple photovoltaic regions with different band gap energies to achieve spectral splitting, then energy conversion efficiency is improved, but device complexity increases
Solution Approach 1:
The solar cell is divided into multiple photovoltaic regions (first, second, and third photovoltaic regions) with different band gap energies, where each region converts photons in specific wavelength bands to electrical current. This segmentation enables spectral splitting while maintaining manageable device complexity through systematic design of individual regions with specific functions.
Solution Approach 2:
The patent employs III-V compound semiconductor materials with carefully selected band gap energies for different photovoltaic regions. By using composite material structures with complementary band gaps, the device achieves high energy conversion efficiency through spectral splitting while the material system itself provides a framework that manages the complexity of multiple regions.
2Power
If the top subcell covers the entire surface, then current collection from the top subcell is maximized, but the second subcell cannot directly receive incoming light
Solution Approach 1:
The top subcell is segmented to cover only a portion of the surface area, leaving exposed portions where the second subcell can directly receive incoming light. This spatial segmentation allows both subcells to function simultaneously - the top subcell collects current from its covered area while the second subcell captures light in the exposed areas, maximizing overall energy utilization.
Solution Approach 2:
The patent transitions from a single-layer coverage model to a multi-dimensional spatial arrangement where the top subcell and second subcell occupy different spatial zones on the solar cell surface. This dimensional differentiation enables both subcells to perform their respective functions without mutual interference, with the top subcell handling photons in certain wavelength bands and the second subcell handling photons in other bands that pass through or are directed to its exposed regions.
3Manufacturing precision
If lattice matching is strictly maintained between semiconductor layers, then manufacturing precision is improved, but adaptability in optimizing band gaps and doping levels is reduced
Solution Approach 1:
The patent employs III-V compound semiconductor materials where composition parameters can be adjusted to achieve desired band gap energies while maintaining lattice matching. By changing material composition ratios within the III-V system, the design optimizes band gaps for different photovoltaic regions without sacrificing lattice compatibility, thus maintaining manufacturing precision while achieving spectral splitting goals.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design increases the current collection in the second subcell, matches current levels between beginning-of-life (BOL) and end-of-life (EOL), and enhances power output by optimizing the band gaps and doping levels, resulting in improved radiation hardness and efficiency over the solar cell's operational life.
Implementation Method 1
Each subcell is designed to convert photons over different spectral or wavelength bands to electrical current
Implementation Method 2
After the sunlight impinges on the front of the solar cell, and photons pass through the subcells, with each subcell being designed for photons in a specific wavelength band
Data Source
AI summary
A multijunction solar cell including an upper first solar subcell having a first band gap and positioned for receiving an incoming light beam; a second solar subcell disposed below and adjacent to and lattice matched with said upper first solar subcell, and having a second band gap smaller than said first band gap; wherein the upper first solar subcell covers less than the entire upper surface of the second solar subcell, leaving an exposed portion of the second solar subcell around the periphery of the multijunction solar sell that lies in the path of the incoming light beam.